1. Field of the Invention
The present invention relates to an injection device. More particularly, the present invention relates to an injection device in which a pelletized resinous material is fed into an injecting portion via a material feeding portion and in which the resinous material is melted in the injecting portion and is then injected into a molding die.
2. Description of Related Art
A known injection device is taught, for example, by Japanese Laid-open Patent Publication Number 2002-307485. In this known injection device, a material feeding passage is vertically formed in a material feeding block. The material feeding block has a hopper that is attached to an upper end thereof, and a heating cylinder that is attached to a lower end thereof. The hopper contains a pelletized resinous material therein. The heating cylinder functions as an injecting portion. The pelletized resinous material contained in the hopper can be fed into the heating cylinder by gravity via the material feeding passage. The pelletized resinous material fed into the heating cylinder can be melted in the heating cylinder to form a molten resinous material. The molten resinous material can be injected from the heating cylinder (the injecting portion) into a mold.
Further, the material feeding block has a bridge breaker that is capable of preventing the pelletized resinous material from being bridged. The bridge breaker has a push-in passage that is communicated with an interior of the heating cylinder via a lower end portion of the material feeding passage, and a breaker plunger that is capable of reciprocating within the push-in passage. Due to actuation of the breaker plunger, the pelletized resinous material can be smoothly pushed into the heating cylinder. Thus, the pelletized resinous material can be effectively prevented from being bridged in the material feeding passage.
However, in the known injection device, the pelletized resinous material can be fed into the heating cylinder (the injecting portion) by gravity. Therefore, the pelletized resinous material cannot be completely prevented from being bridged in the material feeding passage. That is, the pelletized resinous material can sometimes be bridged in the material feeding passage to form a bridged resinous material therein. The bridged resinous material thus formed cannot be easily broken even if a force is applied thereto by the breaker plunger. This is because the force applied by the breaker plunger is a single directional force. As a result, the bridged resinous material cannot substantially be pushed into the heating cylinder by the breaker plunger. This may lead to clogging of the material feeding passage caused by the bridged resinous material.
In addition, the pelletized resinous material can be fed into the heating cylinder (the injecting portion) by gravity. That is, the pelletized resinous material can be transferred downwardly (i.e., in a direction of gravitational force) toward the heating cylinder. Therefore, the injection device can be restricted from a standpoint of design. For example, the injection device must be designed such that the heating cylinder can be transversely or horizontally positioned. If the heating cylinder is vertically or obliquely positioned, the pelletized resinous material cannot be stably and reliably fed into the heating cylinder. As a result, the molten resinous material formed in the heating cylinder cannot be sufficiently and uniformly injected from the heating cylinder into the mold. This may lead to considerable variation in quality of a molded article formed in the mold.
Thus, there is a need in the art for an improved injection device.